1. Field of the Invention
This invention relates to the control of a fluid flow. More specifically, it relates to the direct, precise, and independent control of momentum and swirl entering into the fluid system.
2. Brief Description of the Related Art
In past studies, flow control has been implemented to improve the performance of aerodynamic bodies in terms of lift increase and drag reduction, to increase mixing in combustion processes, and to reduce noise from moving bodies. Enhanced performance is primarily accomplished by reducing the size of the region with flow separation. The root of flow separation over a body stems from boundary layer separation, [1], [2] especially for flows exposed to adverse pressure gradient [3], [4]. Depending on the geometry and flow conditions, the separated boundary layer can either remain separated over the length of the body or reattach downstream. The separated flow region is detrimental to on the performance an airfoil. Therefore, the fundamental goal of flow control, in general, on an airfoil is to deter the boundary layer from separating. Flow control devices attempt to increase the momentum in the boundary layer to oppose the adverse pressure gradient. With appropriate control effort, the flow can remain attached over the entire suction surface of the airfoil, thus enhancing performance.
Flow control actuators are utilized to introduce perturbations to the flow, and can be categorized into two types of devices: active and passive actuators [5], [8]. Active flow control is defined as the addition of energy to the flow. A large assortment of active flow control devices are discussed in the review by Cattafesta and Sheplak [6]. Active flow control devices include steady blowing/suction [3], [9], synthetic jets [10], plasma actuators [11], vortex generator jets [12], [14], and others. Passive flow control devices modify the flow without the need of energy input. Specific types of passive actuators consist of wavy leading edge [15], vortex generators [16], [17], and riblets [18], [19]. These devices listed above do not encompass all of the devices that have been developed, but give an idea of the extent of the variety of actuators that have been developed.
Numerous works have been performed for both laminar [20], [21] and turbulent [19], [22], [24] boundary layer control. Additional focus has also been placed on controlling the transition of a boundary layer from laminar to turbulent [25], [26]. While there are a wide variety of flow control devices available, what the surrounding flow receives from the actuators can be simply considered as a combination of mass, momentum, vorticity, or energy. The present invention includes momentum and vorticity injection to alter the separated flow over an airfoil. Momentum injection reattaches the flow by adding momentum directly to the boundary layer. Vortex generators pull high momentum fluid from the free stream [27]. Due to inherent coupling, there is also an inherent momentum injection related to vortex generators due to the geometry deflecting the flow.
One major drawback of the existing flow control actuators is associated with their incapability to control the actuation momentum and swirl separately. Flow control actuators currently known in art are only capable of providing a fixed combination of the momentum and swirl, with most commonly used actuators focusing exclusively on linear momentum injection.
Accordingly, what is needed is method of controlling fluid flow by introducing momentum and swirl (or vorticity) into the flow and adjusting the momentum and swirl independently to alter the characteristics of the fluid flow. However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.
All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
The present invention may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that the invention may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed invention should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.